System.Data.SQLite

I've a db with three tables. 

images = wich contains the info of the image.( id | filename | width | height | private | ... )

nodes = wich contains the image id and the tag id. ( image_id | tag_id | private )

tags = wich contains tags. ( id | tag )

The user can select the images seaching by tags using :

SELECT images.* FROM images INNER JOIN nodes ON images.id = nodes.image_id WHERE tag_id IN (SELECT tags.id FROM tags WHERE tags.tag IN ('tag1','tag2')) GROUP BY images.id HAVING COUNT(*) = 2

The problem is that i've nearly 50,000 entries on images table, the nodes table contains 452,299 entries and the tags table contains 4,612 entries.

Now, the problem is that i try to retrieve 5000 images i've to wait almost 7 minutes to have all results :S

The tables don't have primary keys, only the tags table, because the data is stored using the ids of the images downloaded from a website, so i cant set autoincrements on images table or ser a primary key because the user can download the images and also add his owns setting if it is private on tables images and nodes (private as char = "n" or "y")...

So how can i increase the select speed? Increasing pragma?  cache? i'm really new on sqlite and don't have enough knowledge about it.

Just in case you haven't thought of this, make sure you have an index created on any field you are looking for in a WHERE clause.  If you don't have an index, then it has to look through all of the records...

And how i can create an index non unique for the image table from vb.net?

I'm using a tool called NAVICAT which has a GUI interface to do it.

I think the SQl command is something like: create index idx_tag on tags (tag) asc

documentation: 

 http://www.sqlite.org/lang_createindex.html

I think you'll also need an index on the nodes table as well:

create unique index idx_tag_id on nodes (tag_id) asc

 Basically you need an index on anything after a where clause if its not the primary index.

 Yes, thank you. I've created a lot of indexes to solve thhis issues but is working fine. I ussualy use SQLite administrator.